Acoustic-Emission-Monitored Tests for TAB Inner Lead Bond Quality

An introduction to acoustic-emission (AE)-based tests applied to quality control in the electronics industry is given. Bond integrity tests for tape automated bonding (TAB) devices using AE monitoring are described. These include a pull tester and a microfatigue tester for off-line evaluation of bond quality and metallurgical system reliability as well as a prototype of an automatic on-line production bond quality tester. The microfatigue tester for TAB leads can apply a small oscillatory (up to 80 Hz) force on top of a constant force bias of a few grams. A major result was that the most common metallurgical system (tin-plated copper leads bonded to gold bumps) results in the formation of brittle intermetailic compounds which crack relatively easily. The cracks propagate under cyclic stress and result in a very low fatigue life, compared to another TAB metallurgical system. The inner lead bond integrity tester and lead-forming system is designed to be used on-line. Precision tools apply a predetermined force to the leads, which nondestructively tests the bonds and forms the leads. The AE monitor can indicate any failures and the device can be rejected.